During the transmission of high-speed signals, energy reflection of high-speed signals causes EMI (Electromagnetic Interference), i.e., electronic noise which interferes cable signals and damages signal integrity. EMI is usually caused by a source of electromagnetic radiation, such as a motor or a machine. EMI can be classified into two types, i.e., conduction interference and radiation interference. The radiation interference needs to be reduced in the technical field of spread spectrum decoding of a display device. Radiation inference means that an interference source couples a signal thereof to another electrical network through space. If radiant energy is too high, it will cause damages to human body. In the TFT-LCD (Thin Film Transistor Liquid Crystal Display) industry, data signal transmission and high-speed signal transmission also have the risk of EMI. Thus, reducing EMI is a burning technical problem to be solved.
In the prior art, spread spectrum technology is a commonly-used wireless communication technology. When a clock generator on a mainboard works, pulse peaks will cause EMI which can be reduced by spread spectrum technology.
Spread spectrum function periodically modulates and demodulates crystal oscillator frequency of a fixed input signal frequency of high-speed signals (Fclkin). Spread spectrum wave form is shown in FIG. 1. TFT-LCD data signal are all high-speed signals. LVDS, V-by-One, mini-LVDS, and USI-T are all common TFT-LCD data signals.
Spread spectrum function of LVDS (Low-Voltage Differential Signaling) is taken as an example below for illustration.
In an electric furnace, LVDS is configured to transform a serial signal into a parallel signal of a TTL (Transistor-Transistor Logic) level signal, and send the parallel signal to a LCD screen for sequential control and to form a row driving signal and a column driving signal. A LVDS signal is a low-swing differential digital signal which appears in pairs. A LVDS circuit transforms a TTL digital signal, a clock signal, a horizontal synchronous signal, and a vertical synchronous signal into LVDS signals through coding, drives a current source through a differential line, and sends the LVDS signals into a differential receptor of a TCON (Time Control Register). Upon receipt of the LVDS signals, the TCON decodes them.
Normally, LVDS signals used in a TFT-LCD have a fixed input signal frequency of 75 MHz. A maximum floating range (variation range) of the input signal frequency is ±2%, while the spread spectrum has a variation frequency of 200 KHz, i.e. varying in a range of 73.5 MHz to 76.5 MHz.
The input signal frequency changes in a regular pattern, i.e. the input signal frequency gradually increases from 73.5 MHz to 76.5 MHz and then gradually decreases from 76.5 MHz to 73.5 MHz. The foregoing process is repeated again and again. A frequency change speed shall not have a cycle above 200 KHz.
The above method effectively reduces EMI. However, it makes decoding work of the TCON after receipt of a signal become difficult, which causes risks of signal decoding error and display noise and eventually affects image quality.